Semiconductor wafers or substrates, such as silicon wafers, may include nitrogen. The nitrogen may be introduced into the wafer either intentionally or unintentionally. For example, the wafer may intentionally be doped with nitrogen, such as by introducing nitrogen into the molten material from which an ingot is drawn and from which wafers are subsequently cut. Nitrogen may also diffuse into a wafer at various stages of the fabrication process. For example, the wafer may be annealed or otherwise processed at an elevated temperature in an environment that includes nitrogen, thereby causing nitrogen to diffuse into the wafer.
Regardless of the manner in which a wafer is doped with nitrogen, it is oftentimes advantageous to determine the concentration of nitrogen within the wafer since the presence and, more particularly, the concentration of nitrogen within the wafer affects at least some of the properties of the wafer. For example, the presence of nitrogen serves to encourage the precipitation of oxygen in the bulk portion of a wafer. In this regard, the nitrogen serves as nucleation sites for oxygen, thereby accelerating oxygen precipitation in the bulk portion of a wafer. By encouraging the precipitation of oxygen within a wafer, the resistivity of the wafer can be tailored and may have a relatively high resistance as described by co-pending U.S. patent application Ser. No. 10/008,404, filed Dec. 6, 2001, entitled High Resistivity Silicon Wafer Having Electrically Inactive Dopant And A Method Of Producing Same, the contents of which are incorporated in their entirety herein.
Conventionally, the nitrogen concentration of a wafer has not been directly measured from the wafer. Instead, an estimate of the nitrogen concentration of the wafer would generally be established based upon the concentration of nitrogen available as a dopant during the fabrication of the wafer. For example, the eventual concentration of nitrogen within the wafer may be estimated based upon the concentration of the nitrogen provided as a dopant in the molten material from which an ingot is drawn and from which the wafer is thereafter sliced. Alternatively, the concentration of nitrogen within a wafer may be estimated based upon the concentration of nitrogen in the surrounding environment while the wafer is being annealed or is otherwise subjected to elevated temperatures.
As will be apparent, estimates of the nitrogen concentration within a wafer based upon the nitrogen concentration that was provided as a dopant during the process of fabricating the wafer may not be entirely accurate. With the increased specificity with which wafers and their properties are being defined by the microelectronic industry, it would be desirable to determine the concentration of nitrogen within a wafer with greater specificity. As such, it would be desirable to develop a method for more accurately and directly measuring the concentration of nitrogen within a wafer.